Control and indicating system for scrubbing gases with scrubber liquor



July 16, 1957 GASES WITH SCRUBBER LIQUOR 2 Sheets-Sheet l Filed May 24,1954 s E Q mw mo mo. .m njooo mm WB l A Nm m N R SEDE 'BY HMLJ @.v. nu

EHU..

July 16, 1957 R. B'. MOORE CONTROL. AND INDICATING SYSTEM FOR scRUBBINGGASES WITH SCRUBBEIR LIQUOR Filed May 24, 1954 2 Sheets-Sheet 2THERMOCOUPLE LEADS COPPER LIQUOR :NLET/ S PAcKlNG MATERIAL FIG. 2.

JNVENTOR. l

R. B. MOORE Y ATT RNE Unite ratesY Patented July 16, 1957 CONTROL ANDINDICATLIG SYSTEM FR SCRUBBING GASES WITH SCRUEESER LIQUOR Robert B.Moore, Washington, D. C., assigner to ihiiiips Petroleum Company, acorporation of elaware Application May 24, 1954, Serial No. 431,56r

3 Ciaims. (Cl. S40- 237) This invention relates to an indicating systemfor detecting faulty operation of a scrubber wherein carbon dioxide,carbon monoxide and other materials are removed by an ammoniacal coppersolution from a stream containing nitrogen and hydrogen, In anotheraspect, it relates to an indicating and control system for suchscrubber. In still another aspect, it relates to an absorption vessel ofimproved construction provided with a tcmperature-determini-ng element.

In the synthesis of ammonia from mixtures of hydrogen and nitrogen, araw synthesis gas is prepared containing hydrogen and nitrogen, usuallyin stoichiometiic proportions for the formation of ammonia, togetherwith carbon monoxide and carbon dioxide, this raw synthesis gas beingproduced, for example, from methane and air. This gas is ordinarilysubjected to a catalytic reforming operation wherein the buik of thecarbon monoxide is converted to carbon dioxide, and the carbon dioxideis then removed by scrubbing with water or other suitable material.

Even after such treatment, however, there is some carbon monoxide leftin the synthesis gas, and it is important that this material be removedprior to the catalytic reaction of the nitrogen and hydrogen to formammonia, as carbon monoxide is an effective poisoning agent for thecatalyst used in the ammonia synthesis reaction.

One way in which the residual carbon monoxide together with carbondioxide is removed commercially is by treating the gas passing from thecarbon dioxide scrubber with an ammoniacal copper liquor which, in itsreduced state, can be represented by the following formula: Cu(NH3)n+Rand, in the cupric state, by the equation Cu(NHs)2n++R- where n is asmall integer, such as 2, and R represents a suitable ion, such as theformate `or carbonate ion. At low temperatures, this material, hereafterreferred to as copper liquor, has the property of absorbing carbondioxide and carbon monoxide from the synthesis gas. After thus absorbingcarbon dioxide or carbon monoxide, the copper liquor can be regeneratedby heating it, whereupon the oxides of carbon are released and thecopper liquor, after cooling, is ready for reuse in the absorption zone.

In the past, diliculties have arisen in the operation of such scrubbersresulting in insucient absorption of the carbon monoxide or carbondioxide from the ammonia synthesis gas. This has serious results uponthe operation of the ammonia synthesis system since even small amountsof carbon monoxide have a definite and deleterious poisoning eiect uponthe ammonia synthesis catalyst.

In particular, insufficient absorption may occur as a result ofincreased carbon monoxide or carbon dioxide concentration in the inletgas, a decrease in ammonia or cuprous copper concentration in theliquor, or a decreased ow rate of the copper liquor through theabsorpton vessel. Insuliicient absorption of the carbon monoxideresulting from any of these causes is difficult to detect, and mayresult in poisoning of the synthesis catalyst unless prompt correctiveaction is taken. While poor regeneration of the copper liquor orinsuicient cooling thereof can also result in insucient absorption,these difliculties seldom result in poisoning of the synthesis catalystsince they occur infrequently, and can be readily detected with thecontrol instrumentation ordif narily provided in such systems. v

However, insuficient Iabsorption resulting from any of the rst fourcauses is very diicult to detect, and often results in poisoning ordamage to the synthesis catalyst before the trouble is detected incommercial operation.

lt is an object of this invention to provide an indicating system whichwill promptly warn the operator of a copper liquor scrubber of anincreased concentration of carbon monoxide or carbon dioxide in theinlet gas, a decrease in ammonia or copper concentration in the copperliquor, or a lack of suicient copper liquor ow for the volume of gasbeing treated.

it is a further object of the invention to provide an automatic controlsystem which will temporarily alleviate the condition causinginsuflicient absorption, and promptly warn the operator so that thecondition can be remedied, thus avoiding poisoning of the ammoniasynthesis cata-l lyst.

A further object of the invention is to provide an absorption vessel ofimproved character embodying a temperature sensing device.

Various other objects, advantages and features of the invention willbecome apparent from the following detailed description taken i-nconjunction with the accompanying drawings, in which:

Figure l is a flow diagram of a copper liquor scrubbing sytem embodyingthe indicating and control system of the invention; and

Figure 2 is a vertical sectional view of the top portion iof theabsorption vessel constructed in accordance with the invention.

Referring now to the drawings in detail, and particularly Figure l, Ihave shown an absorption system including two absorption towers 10 andl1, the detailed construction of which will be hereinafter set forth .indetail. It will be understood that, although two absorption vessels areshown, the principles of the invention are applicable to absorptionsystems including one, three, or even more absorption vessels, as willbecome apparent to those skilled in the art. The gas to be treated,which is a mixture of hydrogen and nitrogen, usually in stoichio metricproportions for the formation of ammonia, and containing carbonmonoxide, carbon dioxide, and possibly some oxygen is fed through avalved line 12 to the vessel i@ and through a valved line 13 to thevessel 11. The vessels il@ and 11 are preferably packed columns and, asshown in connection with vessel 19, contain suitable packing material14, such as Raschig rings or Beryl saddles, which are supported adjacentthe bottom of the column by a grid 15. Y

Regeneratcd copper liquor from a conduit *in enters the vessels iti andil through valved lines i7 and "3, respectiveiy. ln the absorptionvessels fr@ and ii, the acsending impure synthesis gas is contacted withccuntercurrently iiowing copper liquor solution, treated gas leaving thevessels it? and il through valved lines i9 and 20, re-

spectively, and passing through a conduit 2i to a suitable f utilizationsystem, such as an ammonia synthesis unit.

The spent copper liquid leaves the vessels 1G and 11 through valvedlines .'23 and 24, respectively, from which the spent liquor passesthrough a conduit 2S to a regenerator 27. A heating medium enters theregenerator 27 Conduitto a stachf or other suitable disposal. Theregenerated copperliquor emergestfromthe vesselY 27' through a line 30and passes to a cooler 31 and a storage vessel 32. From the vessel 32,the regenerated liquid passes-to-conduit-l'', the-rate of flowbeing-d'eternti'ncdjbyA a. controller- 34having-a pair; of"owsensingunits 3:5" and 36' mounted at the opposite sidesY of an`critico in the conduit 1,6. A motorA valve 38 ini-conduit 16 is actuatedby rthe controller 34' to maintain a predetermined rate. of flow of thecopper liquorthrongh the absorption' vessels andi 1'1;

` A conduit 319'by-passes the-controller 34 and valve 38; this'conduithaving a solenoid valve 4t`t disposed4 therein which controls the iiowof material. therethrough. This valve is closedih normal operation ofthe. system, but is opened'` automatically when insuli'ci'ent absorptionof` the carbon 'oxides from'the synthesis gas takes place Vin thevessels 1,0, andii'l, asiwillibe explained Vin detail'hereafter.

.Ul-.aye discoveredthanwhen insucient absorption of' the carbon oxidestakes place, a temperature riseY results in. the-bedof packing material14 inthe. absorption vessel ata denite and predeterminable. distancefromme bottom of i the, absorption. bed, Such a temperature change,takesplace Vas a. result of increased carbon. monoxide. or carbonYdiogtide concentration in the-inletigas, a; decreasein the ammoniaconcentration of the copper liquor, a decrease, in, the coppercontent oftheV liquor-,or alacleosuicientcopper liquor. ow tol takeA care. of; thequantity. of4 synthesisgas passing through the absorption vessel. Any ofthese conditionscan, inlaccordance:withthe` invention,heroinedied;temporarilyr by increasing the rate oiiiow of, copper-lliquor throughthe system. i Also,V at the time; the conditioncausinginsuicient absorption occurs, analarm, s-,sounded-.soithat thecondition can be. promptly remedied beforeftheytemporary correctioneffected by'increasing the` iiow of copper liquor becomes ineffective. n

Accordingly, in reach* of the vessels'10-and11, I haveV provided alpipe43 which. extends downwardly into. the` absorption vessel to apredetermined distances Dimmi theabottomgof the bedof;packingjmaterial... A thermocoupleAfi; is: mounted-at the bottomof1thefpipe43Y to.l

Sense; thea temperature. in z the pack-ing. at, thispoint. The

' therm0couple;44 isfconnectedbyfleads 45Yandf46together witha: switchy47 tov an-electroniccontroller: 48. Switchl 47;isoperable to.connectthe-.inputcircuit of electronic controller` 45am-a similarthermoeouplmnotshown, inV

vessel: 1I which, has; leads. 49; and 501` connectedthere-to.-v

Switchz 4f73'can1be sequentiallyl operated,v inA accordanceywithitheinvention, tOsequentially monitor the -temperature aselecteddistancev above the bottom-fof the bed-of absorption material inv therespective absorption vessels.

The controller148 has a; shaftr, theangular position4 ofi'which isrepresentative; of theY temperature sensed; by the thermocoupleunitvconnected thereto. shaft-l53isza pointer 54 which, is'engageable-with-:acontact '55 when the temperature" sensed by=thegthermocouple exceeds a`predetermined value. Tlrefpointer- 54V andcontact 55 :are connected incircuit witlrfthe-operating winding of a relay 56'and a battery S7, therelay.v 56 Vbeing provided with a holding circuit through'a set 58 ofnormal open relaycontacts, and a lead 59.

The relay 56 has an additional set ofnormally open contacts 60`which areconnected; in circuit with a battery 61` andan alarm 62, suchas'abellior whistle. Finally, relay 56 has a set 65 of normallyopencontacts which are connected in circuit with abattery fandthe;operatture-of-the-copper liquor is approximately 0: CL, andzthezYoutlet-'temperature isf between 16v and'20." C.. DuringV normaloperation, theA temperature mid-.wayl between Y the end-of 'the-packingis less than: 12 C.. but, whenf insui'- cient :absorption-occurs', dueto thefcausesfalready,stated,.

Attached to the temperature rises above 12 C. at this region. Thus, inthis particular installation, controller 48isrsetto-close the circuitbetween indicator 54 and contact 55 when the temperature exceeds 12` C.at the thermocouple.

In the operation of the system, relay 56 is deenergzed, and pointer 54is not in engagement with contact 55, due to the fact that thetemperatureVl of thermocouple 44 is below 12 C. However, `should there:be anjincrease` in they carbonmonoxide or carbon'. dioxide concentrationin the inlet gas, a decrease in ammonia or copper. concentration. in thecopper liquor or a lacleof suficientcopper liquor ow to: eiectivelyabsorb' the' oxides. of carbon from the synthesis gas, the temperatureat tliermocouple 44 rises above thepredetermined valuezofglZ C. As aresult, the operating circuit. of relay 56. is closed, andL remainsclosed due to the action ofVV the holding circuit 57, S8 and 59.Responsive tothe energization of relay 56, the alarm 62 is actuatedythrough closure of contacts 6i), and'tsolenoid valve 40isopened`byactuation of contacts 65.;` Accordingly, dueto `the .fa'ct"that'line 39jis larger than conduit-16; there isa substantial increase" in flow *ofVVcopperliquor to the scrubbing vesself Itf isa feature of the inventionthatthe operation of' the' indicating and control system isv so. rapidthat the condition causing'insuicient' absorption can be readily'corrected before'any gascan leavethe' absorption vesselv whichiscontaminated withcarb'on monoxide or carbon dioxide; Alternatively, ifthe' automatic' control feature o'the systemv is not utilized, an alarm62 is sounded` in" time for'theoperator to correctfthe condition, againbefore any of the gas contaminated with carbon monoxide or carbondioxide can leave the absorption vess'elj,`

' It willbe notedthat, with two absorption vessels, switch".V 47c-an.beautomatically actu-ated to alternately transfer n the connect-ion ofVelectronic cont-roller to the thermocouple 44'and`vessel 10 andto. thesimilar thermocoupie in vessell; Controller 48automaticall`y indicateswhich ther-mocouple was connected thereto when operation of theVautomatic control system takes place.

Accordingly, [have achieved theobject-s ofmy invention inpermittingiinsuilicient absorption to be promptly 'and automaticallydet-ectedland the condition corrected before the contaminated" gasleaves the',absorptionvessel.L As` previously noted, no warningorcontrol action is provided by, theV systemwtltiere the cause Vofinsuicient absorption is poor` regeneration ofth'e copper lliquor orin'suliicient'A cooling thereof. However, suchcondit-ions can' be readIily detected by the normal instrument-ali-ties to permit them to belcorercted before contaminated gas leavesV the absorber: i,

`As stated, withaZO' foot bed, in one'commencial ins-tallation, thethermocouple hasbeen located half-wayf down. inthe bed, i. e., lO'fe'etfrom the bottom ofthe bed'. Ot' course, the optimum point of' locationon .the.t-herrrio` couple varies with differentinstallatitmsgY an'dtheproper' loc-ation can" b'e readily determined experimentally. In" somecases, the defined temp erature control can beeiect'ed' by measuring thetemperature ditfferentialvacross the top,"

considerable iiuctuatiom, arenot to be. preferred where the. normalytreatment temperaturel remains-.-st-able..

lnFignre 2, I havey shown an improvedtabsorptionvese sel provided. withAa .thermowelland athermocoupleofithe characterA describedinconnectionwithFigure.. LY Tliis vessel. includes 'acylindrical.laminatedv4 wal=L70 within.. whichisdisposed: packing material.7\1..,A..htavy;coverA plate 72is secured to the head. 73 -of.the.vessel',land.thegas.

outlet conduit 19 prot-rudes. laterallyy throughthe. headllandisconnectedwith a: mist entr-actor 74th-rough cwhiolt.

thetreated gases pass tout 'of the; system. f The copper liquor inlet."17 also. protrudes.. laterally,throughn the.` head '773,v

and communicates with a spray nozzle 75 located centrally of the crosssection of the vessel.

A thin Walled tube 76 is secured to the shell of the vessel by supports77 and 78, this tube extending about half-Way down into the packingmaterial 71. A thermo- Well 80 is mounted concentrically Within the tube76 and extends to the bottom thereof where the thermocouple 44 islocated. The thermowell 80 extends through an opening 81 formed in thecover plate 72, and it is received Within a flange S2 secured to thecover by bolts 83. A sealing gasket 84 is interposed between the ilange82 and the cover 72. Thus, the thermowell extends vertically from thetop ofthe vessel down into the packing in an area not occupied by themist extractor 74. In this manner, it is not necessary to provide anopening through the laminated and stress relieved sides of the vesselA70, yand it is not, of course, possible to insert the thermocouplethrough the inlet or outlet pipe, which would necesitate a 90 bendin-the thermo- Well, and prohibit installation of the thermocouple.However, With the installation, .as shown, extremely satisfactoryresults are obtained, no diiiiculty is encountered i-n properly sealingthe vessel, and the thermocouple can be readily inserted into place orremoved for repair or replacement.

While the invention has been described in connection With a present,preferred embodiment thereof, it is to be understood that thisdescription is illustrative only and is not intended to limit theinvention.

I claim:

1. An indicating and control system for a copper scrubber whichcomprises, in combination, an absorption vessel, packing material insaid vessel, a source of gas including nitrogen, hydrogen, carbonmonoxide, and carbon dioxide, means for feeding gas from said source tothe bottom of said absorption vessel, an effluent line connected to thetop of said absorption vessel to Withdraml gaseous eiiluent therefrom, aregenerator, a valved line connected to the bottom of each absorptionvessel and communicating with the inlet of said regenerator, means forpassing a heating medium in indirect heat exchange with the material insaid regenerator, a conduit connecting the outlet of said regenerator tothe top of said absorption vessel, means for circulating copper liquorthrough said vessel, said regenerator, and said conduit, a rate of ilowcontroller in said conduit to provide a predetermined rate of flow ofcopper liquor to said vessel, a line by-passing .said rate of flowcontroller, a solenoid valve in said by-pass line, a thermocouplepositioned in the packing material of said absorption vessel, anelectronic controller, means for connecting said thermocouple `to theinput of said electronic controller, a relay, an indicator connected tosaid controller and responsive to the output thereof, a contactengageable by said indicator, a circuit including said indicator, saidcontact, a `current source, and the operating Winding of said relay, aholding circuit connected to the operating Winding of said relay, saidrelay having two sets of normally open contacts, an alarm, a circuitincluding a current source connecting said alarm in circuit With S `oneof said sets of normally open contacts, and a circuit including acurrent source connecting the solenoid of said valve with the other setof normally open relay contacts.

2. An indicating and control system for a copper scrubber whichcom-prises, in combination, an absorption vessel, packing material insaid vessel, a source of gas including nitrogen, hydrogen, carbonmonxide, and carbon dioxide, means for feeding gas from said source tothe bottom of said absorption vessel, an eliluent line connected t0 thetop of said absorption vessel to Withdraw gaseous eiuent thereirorn, aregenerator, a valved line connected t-o the bottom of said absorptionvessel and communicating with the inlet of said regenerator, means forpassing a heating medium into indirect heat exchange with the materialin said fregenerator, a conduit connecting the outlet of saidregenerator to the top of said absorption vessel, means for circulatingcopper liquor through said vessel, said regenerator, and said conduit, arate of ilow controller in said conduit to provide -a predetermined rateof ow of copper liquor to said vesesl, a line by-passing said rate ofilow controller, a solenoid valve in said line, a thermocouplepositioned in the packing material in said absorption vesesl, anelectronic controller, means for connecting said thermocouple to theinput of said electronic controller, an alarm actuated by saidelectronic controller, and a circuit connecting the output of saidcontroller to said solenoid Valve, said controller actuating said alarmand opening said solenoid valve when the thermocouple temperature risesabove a predetermined vaiue.

3. An indica-ting and control sy-stem for a copper scrubber whichcomprises, in combination, an absorption vessel, packing material insaid vessel, a source of gas including nitrogen, hydrogen, carbonmonoxide, and carbon dioxide, means for feeding gas from said source tothe bottom of said absorption vessel, an eiiluent line connected to thetop of said absorption vessel to Withdraw gaseous effluent therefrom,means for withdrawing spent copper liquor from the bottom of saidvessel, regenerating said spent copper liquor, `and feeding it to thetop of said absorption Vessel, a thermocouple positioned in the packingmaterial in said absorption vessel, `an electronic controller, means forconnecting said thermocouple to the input of said electronic controller,means controlling the rate of flow of regenerated copper liquor to saidvessel, an alarm, and a circuit connecting the output of said controllerto said controlling means and said alarm, said controller energizingsaid alarm and increasing said ra-te of flow of copper liquor when thetemperature of said thermocouple rises above a predetermined value.

References Cited in the le of this patent UNITED STATES PATENTS1,088,611 Neubauer Feb. 24, 1914 11,578,666 Katz Mar. 30, 1926 1,992,747Gilliland et a1 Feb. 26, 1935 2,047,550 Dely July 14, 1936 2,400,923Farr et al. May 28, 1946

1. AN INDICATING AND CONTROL SYSTEM FOR A COPPER SCRUBBER WHICHCOMPRISES, IN COMBINATION, AN ABSORPTION VESSEL, PACKING MATERIAL INSAID VESSEL, A SOURCE OF GAS INCLUDING NITROGEN HYDROGEN CARBONMONOXIDE, AND CARBON DIOXIDE, MENS FOR FEEDING GAS FROM SAID SOURCE TOTHE BOTTOM OF SAID ABSORPTION VESSEL, AN EFFLUENT LINE CONNECTED TO THETOP OF SAID ABSORPTION VESSEL TO WITHDRAW GASEOUS EFFLUENT THEREFROM,AREGENERATOR, A VALVED LINE CONNECTEDED TO THE BOTTOM OF EACH ABSORPTIONVESSEL AND COMMUNICATING WITH THE INLET OF SAID REGENERATOR, MEANS FORPASSING A HEATING MEDIUM IN INDIRECT HEAT EXCHANGE WITH THE MATERIAL INSAID REGENERATOR, A CONDUIT CONNECTING THE OUTLET OF SAID REGENERATOR,TO THE TOP OF SAID ABSORPTION VESSEL, MEANS FOR CIRCULATING COPPERLIQUOR THROUGH SAID VESSEL, SAID REGERNERATOR, AND SAID CONDUIT, A RATEOF FLOW CON-